Published online December 26, 2006
doi:10.1083/jcb.200602050
The Journal of Cell Biology, Vol. 176, No. 1, 77-88
The Rockefeller University Press, 0021-9525 $30.00
© 2006 Habib et al.
The N-terminal domain of Tob55 has a receptor-like function in the biogenesis of mitochondrial ß-barrel proteins
Shukry J. Habib,
Thomas Waizenegger,
Agathe Niewienda,
Stefan A. Paschen,
Walter Neupert, and
Doron Rapaport
Institut für Physiologische Chemie, Universität München, 81377 Munich, Germany
Correspondence to Doron Rapaport: rapaport{at}med.uni-muenchen.de
ß-Barrel proteins constitute a distinct class of mitochondrial outer membrane proteins. For import into mitochondria, their precursor forms engage the TOM complex. They are then relayed to the TOB complex, which mediates their insertion into the outer membrane. We studied the structurefunction relationships of the core component of the TOB complex, Tob55. Tob55 precursors with deletions in the N-terminal domain were not affected in their targeting to and insertion into the mitochondrial outer membrane. Replacement of wild-type Tob55 by these deletion variants resulted in reduced growth of cells, and mitochondria isolated from such cells were impaired in their capacity to import ß-barrel precursors. The purified N-terminal domain was able to bind ß-barrel precursors in a specific manner. Collectively, these results demonstrate that the N-terminal domain of Tob55 recognizes precursors of ß-barrel proteins. This recognition may contribute to the coupling of the translocation of ß-barrel precursors across the TOM complex to their interaction with the TOB complex.
S.A. Paschen's present address is Institut für Medizinische Mikrobiologie, 81675 Munich, Germany.
Abbreviations used in this paper: BNGE, blue native gel electrophoresis; DHFR, dihydrofolate reductase; IMS, intermembrane space; MBP, maltose binding protein; PK, proteinase K; POTRA, polypeptide transport associated; SAM, sorting and assembly machinery; TOB, topogenesis of mitochondrial outer membrane ß-barrel proteins; TOM, translocase of the outer mitochondrial membrane.

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